How Can We Estimate Coastal Currents of Al Jubail?

1. Location of Al Jubail

Al Jubail is a big industrial city located on the eastern side of Saudi Arabia and shares a coastline with the Arabian Gulf. It comprises enormous petrochemical complexes and is an important centre for the oil and gas industry of the country.

It is set against the backdrop of arid desert landscapes that contrast with the blue expanse of the Arabian Gulf. It has a long stretch of sandy beaches and a network of inlets and channels. The local climate is characteristically very hot and dry for most of the year, with rather mild winters.

Marine life in the Arabian Gulf waters off Al Jubail is very diverse. Shallow coastal waters are considered the nursery for many fish species, and the ecosystem is very rich in corals, mollusks, and other organisms. The gulf is also an important shipping route, with several oil tankers and cargo vessels crossing the area.

2. What is the condition of the coastal currents close to Al Jubail?

The coastal currents in the vicinity of Al Jubail are influenced by several factors. The tidal currents are, in one way or another, quite prominent. In the Arabian Gulf, tides have developed into a regular rise and fall because of the gravitational pull of the moon and the sun. Such tidal currents could vary in strength and direction, considering the lunar phase and local bathymetry.

The wind-driven currents also have an important contribution. Regional prevailing winds can push the surface waters and create surface currents. During certain seasons, the northwest Shamal winds can show a notable impact. They have the potential to influence both the direction and speed of surface currents and the mixing of water masses.

The underwater topography around Al Jubail significantly influences the current. The underwater ridges, channels, and shoals would contribute to changing the flow of water. Currents in shallow areas would be retarded while areas with deeper channels would result in accelerating currents, hence resulting in a complex and dynamic current regime.

3. How to observe the coastal water flow of Al Jubail?

Surface Drift Buoy Method: This method involves setting up buoys on the water surface and letting them drift with the currents. These buoys are normally fitted out with GPS or other devices to track their movements. It is by observing the movements of the buoys over time that the direction and speed of the surface currents are determined. This, in turn, limits the resolution to providing information mainly on the surface layer and with rather poor detail on the vertical structure of the currents.

Anchor Ship Method: This involves a ship anchored in a position well within the Al Jubail coastal area. Instruments, like current meters, are mounted on the ship to record water flow around it. The results obtained from this approach can be quite good within a small radius from the vessel; however, covering a large area with a variety of depths all at once is not very practical with this technique.

The Acoustic Doppler Current Profiler (ADCP) is a much advanced and also much more efficient method for measuring coastal current; it applies the Doppler Effect to measure the current velocities at different levels along the water column. A profiler sends acoustic pulses with some frequency into the water, while it measures a shift in frequency of reflections that come back from water in motion. It helps in providing detailed information concerning the vertical profile of the current from the surface into the seabed.

4. How do ADCPs that utilize the principle of the Doppler effect work?

The principle of the Doppler effect is applied in the operation of ADCPs. They have transducers that emit acoustic pulses into the water. Where these sound waves meet the moving water particles, because of the Doppler effect, the frequency of the reflected waves changes. The change in frequency is proportional to the velocity of the water particles relative to the ADCP profiler.

Commonly, ADCPs use several transducers for water velocity measurement in a different direction. By pulsing in various directions and analyzing the frequency shift of the reflected signals, the ADCP meter can work out the three-dimensional water velocity-that is, the east-west, north-south, and vertical directions. It also measures the time taken by the waves to travel from the transducer to the water particles and back. These measurements, together with the frequency shift, are used in the correct determination of speed and direction of the flow at different depths.

5. What is needed to realize a high-quality measurement of Al Jubail coastal currents?

Certain equipment characteristics are expected for deployment at Al Jubail that must be able to offer a high-quality measurement of the currents at the coast. Reliability and resistance against the harsh conditions of the sea will characterize the material property. It will be compact in size with lightweight to ensure the equipment is easily deployable. Also, it has to use low power in order for the operating time to be very long; in particular, in some monitoring cases.

The casing of the ADCP current meter is preferably made of titanium alloy. The corrosion-resistant properties of the alloy are excellent, which is quite crucial in the saline environment of the Arabian Gulf. This material has a high strength-to-weight ratio, indicating that it can provide durability while keeping the equipment relatively light. This material is able to withstand pressure changes associated with different water depths.

6. How to Choose the right equipment for current measurement?

While selecting equipment for current measurement in Al Jubail, consider the following factors.

Depending on the purpose of use, various types of ADCPs can be chosen. For example, a ship-borne ADCP is installed on a vessel and is able to measure currents while the ship is on the move. This will be useful to cover the wide area of the coastal waters. A bottom-mounted ADCP is fixed on the seabed and provides stable measurements of the currents passing above it. It is ideal for long-term monitoring at a specific location. A buoy-mounted ADCP combines the advantages of mobility and ease of deployment, allowing measurements in different areas.

The frequency of the ADCP flow meter depends on water depth: a 600kHz ADCP would be a good option in waters up to 70m, where high-resolution data is returned in shallow waters. For water depths up to 110m, it is more appropriate to have an ADCP with 300kHz. Where the water is deeper, like around 1000m, an ADCP with 75kHz will be recommended for measuring over big vertical range.

There are well-known ADCP brands such as Teledyne RDI, Nortek, and Sontek. However, for a cost-effective option with good quality, the China Sonar PandaADCP is worth considering. It is made of all-titanium alloy material and offers an excellent cost-performance ratio. You can find more information on its website: https://china-sonar.com/.

Here is a table with some well known ADCP instrument brands and moels.